Printing systems typically include one or more input trays for holding media (e.g., paper) with feed mechanisms for picking off one sheet of media at a time and feeding it downstream, a print engine that receives the media from the trays and prints a desired image on the media, and post-printing media handlers that sort, collate, staple, bind, stack, punch or otherwise handle the printed media. Each of the feed mechanisms, print engine, and post-printing media handlers may include several sets of rollers or belts for advancing the media along a media path, which may have an effective length equivalent to the length of several sheets of media. The printing system typically will maximize the overall print processing speed by moving several sheets of media along the media path at any given time. The sheets are tracked by sensors distributed along the path, but typically the sensors are not spaced so closely as to allow one sheet to trip a sensor at all points along the path—blind locations exist along the path.
When a sheet of media is in a blind location between two sensors, one way for the printing system to determine the location of the sheet is to advance the adjacent rollers, belts, or other drive mechanisms, until the sheet is moved to the next sensor. While printing, this occurs in the ordinary course as the drive mechanisms run substantially constantly to advance the media along the media path without concern about whether the sheet is triggering a sensor at any instant of time, other than to set up the next operation in the printing process.
However, under several conditions, the drive mechanisms may be initially turned off, and it may be desirable to detect the presence of media within the media path and to flush it out before continuing with printing. These conditions include: after boot-up of the printing system; after an urgent stop of the printing system, typically caused either by a media jam or a user's opening a sensed door in the printing system; when a device requires a mechanical initialization, i.e., the resetting of its rollers and other mechanics to a home position; and when a device determines that it has a page within its path that needs to be flushed.
The print engine is typically part of a printer which may include a built-in media input tray and which may be coupled to an optional media input device for coordinating media delivery from one or more trays of the media input device to print engine. A given printer may be couplable to several different models of media input device, each model having its own unique, configuration for a media path with one or more sensors and feed mechanisms distributed along the media path. The printer may also have a built-in output tray and be couplable to several different models of media output devices, i.e., collators, binders, etc., each model having its own unique configuration for a media path with one or more sensors and feed mechanisms distributed along the media path.